1. Field of the Invention
The apparatus of this invention relates to detectors for detecting hot boxes on railroad cars, and more particularly to such detectors for automatically scanning journal boxes on railroad cars by passage of the railroad cars within the window of a trackside scanner.
Certain hotbox detectors now in use in the railroad industry provide numerous false indications because of a loss of a background reference. With such hotbox detectors, the trackside scanners are aligned such that the undercarriage or floor of a passing railroad car appears as a background source of reference radiation. Such a background reference is normally near ambient temperature, and it is the difference in temperature between such a background reference temperature and the journal bearing temperature itself, when the journal bearing passes within the detection window of the scanner mechanism and the temperature is detected, that generates a detector output signal.
With certain types of rolling stock now in use there are certain instances when the aforementioned background reference is completely lost as, for example when the hotbox scanner views the sky. When that occurs, the hotbox scanner references on an extremely cold temperature, assuming the sky to be clear, and as the railroad car body comes within the scanner window, the hotbox detector outputs a high output pulse as the normal background reference is re-established. The erroneous high hotbox detector output signal can be of a rather long duration because of the low frequency characteristics of the hotbox scanner itself. If such an erroneous hotbox detector output signal occurs on a moderate to high speed train, it is possible for a journal to pass within the scanner window while the hotbox detector output is still "high" from the change in the temperature reference as discussed above. This results in an erroneous hotbox detector output indication which is the sum of the signal generated by the change of background reference plus the heat pulse from the journal bearing being scanned.
2. Prior Art
U.S. Pat. No. 2,829,267, entitled Hot-Box Detector, discloses an auxiliary shutter actuated by a capacitance-resistance timer circuit to be opened for train speeds effectively exceeding a threshold speed. For lower train speeds, the shutter is closed to prevent saturation or loss of sensitivity of the detector circuitry.
U.S. Pat. No. 2,963,575, Entitled "Hot-Box Detector Alarm Circuit", discloses a gate circuit to assure that the hotbox detector effectively only looks at journal boxes to the exclusion of all other matter passing within the field of view of the detector-response axes. Electromagnetic wheel trips are employed to develop suitable pulse outputs whenever wheel flanges enter the magnetic air gap of the hotbox detector to clearly identify the instant at which each wheel center passes a particular point along the track. Thus, gating only occurs when the detector-response axes are imaged on opposed journal boxes for the same axle. The gate pulses control the entry of temperature data into a capacitance-type storage device.
U.S. Pat. No. 3,313,933, entitled "Integrity Check for Hot Box Detector", discloses an infrared signal for simulating the journals of railway cars, but does not disclose gating circuitry used in conjunction with the hotbox detector circuitry for operating a shutter element to a non-blocking position by successive operation of a wheel detector mechanism. The wheel detector mechanism provides a signal output for the passage of each wheel of a railway car as it passes between a pair of oppositely disposed radiometer detectors. The operation of the gate circuitry prevents extraneous infrared energy, such as solar energy, from being sensed by the hotbox detectors, thereby preventing erroneous detections.
U.S. Pat. No. 3,646,343, entitled "Method and Apparatus for Monitoring Hot Boxes", uses wheel sensors indicating wheel passage to actuate sensors to generate analog signals proportional to the magnitude of the journal heat sensed.
In U.S. Pat. No. 3,731,087 entitled, "Hot Box Alarm System", there is incidental disclosure pertaining to wheel trip sensor circuitry and associated gate circuitry for ensuring that the journal sensors produce signals that indicate the temperature of the journal boxes and not the temperature of extraneous heat-producing objects. However, the particulars of the gate circuitry are not disclosed.